Allergic diseases and conditions, such as asthma, allergic rhinitis, atopic dermatitis, and food allergy, have become increasingly prevalent over the past few decades and now affect 10-40% of the population in industrialized countries. Allergic diseases profoundly affect the quality of life, and can result in serious complications, including death, as may occur in serious cases of asthma and anaphylaxis. Allergies are prevalent, and are the largest cause of time lost from work and school and their impact on personal lives as well as their direct and indirect costs to the medical systems and economy are enormous. For example, allergic rhinitis (hay fever) affects 22% or more of the population of the USA, whereas allergic asthma is thought to affect at least 20 million residents of the USA. The economic impact of allergic diseases in the United States, including health care costs and lost productivity, has been estimated to amount to $6.4 billion in the early nineties alone.
Most allergic diseases are caused by immunoglobulin E (IgE)-mediated hypersensitivity reactions. IgE is a class of antibody normally present in the serum at minute concentrations. It is produced by IgE-secreting plasma cells that express the antibody on their surface at a certain stage of their maturation. Allergic patients produce elevated levels of IgE with binding specificity for ordinarily innocuous antigens to which they are sensitive. These IgE molecules circulate in the blood and bind to IgE-specific receptors on the surface of basophils in the circulation and mast cells along mucosal linings and underneath the skin. Binding of antigen or allergen to IgE on mast cells, basophils, and other cell types, crosslink the IgE molecules, and aggregate the underlying receptors, thus triggering the cells to release vasoactive and neuronal stimulatory mediators such as histamines, leukotrienes, prostaglandins, bradykinin, and platelet-activating factor. The rapid reaction of the immune system to antigen caused by antibody immune complexes has led to the term immediate or antibody-mediated hypersensitivity reaction, in contrast to delayed or cell-mediated hypersensitivity reactions that are mediated by T cells. IgE-mediated immune reactions are specifically referred to as type I hypersensitivity reactions.
The high affinity receptor for IgE (FcεRI) is a key mediator for immediate allergic manifestations. In addition to mast cells and basophils, the primary mediators of allergic reactions, FcεRI is found on a number of other cell types including eosinophils, platelets and on antigen-presenting cells such as monocytes and dendritic cells. An additional receptor for IgE is FcεRII, also known as CD23 or the low-affinity IgE Fc receptor. FcεRII is expressed broadly on B lymphocytes, macrophages, platelets, and many other cell types such as airway smooth muscle. FcεRII may play a role in the feedback regulation of IgE expression and subsequently FcεRII surface expression.
Since IgE plays a central role in mediating most allergic reactions, devising treatments to control IgE levels in the body and regulating IgE synthesis has been of great interest. Several strategies have been proposed to treat IgE-mediated allergic diseases by downregulating IgE levels. One strategy involves neutralizing the IgE molecules by binding the ε-chain of IgE in or near the Fc-receptor binding site. For example, Omalizumab (Xolair) is a recombinant humanized monoclonal anti-IgE antibody that binds to IgE on the same Fc site as FcεRI. Omalizumab causes a reduction in total serum or circulating IgE in atopic patients, which attenuates the amount of antigen-specific IgE that can bind to and sensitize tissue mast cells and basophils. This, in turn, leads to a decrease in symptoms of allergic diseases. Interestingly, serum IgE levels increase after start of therapy because of omalizumab-IgE complex formation and may remain high up to a year after stopping therapy. Consequently, this issue may lead to false-negatives on diagnostic tests and therefore IgE levels must be routinely checked. Accordingly, there exists a need for improved methods and compositions to reduce IgE-mediated diseases and disease symptoms.